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<span id="Shrink_002dwrapping-separate-components"></span><div class="header">
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<span id="Shrink_002dwrapping-separate-components-1"></span><h4 class="subsection">18.9.14 Shrink-wrapping separate components</h4>
<span id="index-shrink_002dwrapping-separate-components"></span>

<p>The prologue may perform a variety of target dependent tasks such as
saving callee-saved registers, saving the return address, aligning the
stack, creating a stack frame, initializing the PIC register, setting
up the static chain, etc.
</p>
<p>On some targets some of these tasks may be independent of others and
thus may be shrink-wrapped separately.  These independent tasks are
referred to as components and are handled generically by the target
independent parts of GCC.
</p>
<p>Using the following hooks those prologue or epilogue components can be
shrink-wrapped separately, so that the initialization (and possibly
teardown) those components do is not done as frequently on execution
paths where this would unnecessary.
</p>
<p>What exactly those components are is up to the target code; the generic
code treats them abstractly, as a bit in an <code>sbitmap</code>.  These
<code>sbitmap</code>s are allocated by the <code>shrink_wrap.get_separate_components</code>
and <code>shrink_wrap.components_for_bb</code> hooks, and deallocated by the
generic code.
</p>
<dl>
<dt id="index-TARGET_005fSHRINK_005fWRAP_005fGET_005fSEPARATE_005fCOMPONENTS">Target Hook: <em>sbitmap</em> <strong>TARGET_SHRINK_WRAP_GET_SEPARATE_COMPONENTS</strong> <em>(void)</em></dt>
<dd><p>This hook should return an <code>sbitmap</code> with the bits set for those
components that can be separately shrink-wrapped in the current function.
Return <code>NULL</code> if the current function should not get any separate
shrink-wrapping.
Don&rsquo;t define this hook if it would always return <code>NULL</code>.
If it is defined, the other hooks in this group have to be defined as well.
</p></dd></dl>

<dl>
<dt id="index-TARGET_005fSHRINK_005fWRAP_005fCOMPONENTS_005fFOR_005fBB">Target Hook: <em>sbitmap</em> <strong>TARGET_SHRINK_WRAP_COMPONENTS_FOR_BB</strong> <em>(basic_block)</em></dt>
<dd><p>This hook should return an <code>sbitmap</code> with the bits set for those
components where either the prologue component has to be executed before
the <code>basic_block</code>, or the epilogue component after it, or both.
</p></dd></dl>

<dl>
<dt id="index-TARGET_005fSHRINK_005fWRAP_005fDISQUALIFY_005fCOMPONENTS">Target Hook: <em>void</em> <strong>TARGET_SHRINK_WRAP_DISQUALIFY_COMPONENTS</strong> <em>(sbitmap <var>components</var>, edge <var>e</var>, sbitmap <var>edge_components</var>, bool <var>is_prologue</var>)</em></dt>
<dd><p>This hook should clear the bits in the <var>components</var> bitmap for those
components in <var>edge_components</var> that the target cannot handle on edge
<var>e</var>, where <var>is_prologue</var> says if this is for a prologue or an
epilogue instead.
</p></dd></dl>

<dl>
<dt id="index-TARGET_005fSHRINK_005fWRAP_005fEMIT_005fPROLOGUE_005fCOMPONENTS">Target Hook: <em>void</em> <strong>TARGET_SHRINK_WRAP_EMIT_PROLOGUE_COMPONENTS</strong> <em>(sbitmap)</em></dt>
<dd><p>Emit prologue insns for the components indicated by the parameter.
</p></dd></dl>

<dl>
<dt id="index-TARGET_005fSHRINK_005fWRAP_005fEMIT_005fEPILOGUE_005fCOMPONENTS">Target Hook: <em>void</em> <strong>TARGET_SHRINK_WRAP_EMIT_EPILOGUE_COMPONENTS</strong> <em>(sbitmap)</em></dt>
<dd><p>Emit epilogue insns for the components indicated by the parameter.
</p></dd></dl>

<dl>
<dt id="index-TARGET_005fSHRINK_005fWRAP_005fSET_005fHANDLED_005fCOMPONENTS">Target Hook: <em>void</em> <strong>TARGET_SHRINK_WRAP_SET_HANDLED_COMPONENTS</strong> <em>(sbitmap)</em></dt>
<dd><p>Mark the components in the parameter as handled, so that the
<code>prologue</code> and <code>epilogue</code> named patterns know to ignore those
components.  The target code should not hang on to the <code>sbitmap</code>, it
will be deleted after this call.
</p></dd></dl>

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